Induction vs Gas Cooking

[mako]

Originally Posted by Dockhead

The risk of shock goes up with DC voltage, and 24v is the highest which is generally considered more or less safe -- as far as I understand. A 48v system, as far as I understand, needs a different level of protection against shock. But fire risk is for sure less with higher voltages, so it's a balancing act. Higher voltage means more efficient power transmission, too.

For larger boats it could be carried all the way to the point where the entire boat is 120/240/230VAC, with the only 12/24VDC being engine starters, auto bilge pumps and pilothouse electronics. With today's arc and ground fault protections, AC systems have reached high levels of safety.

[Dockhead]

So I have received a 5 page email from a famous professor via my niece, on the systems design and risks questions which Auspicious and I were discussing.


I don't have permission to post the letter so I'll just summarize here:


1. He did not like my idea that you can increase reliability by using one system for everything and concentrating resources on making that one system as reliable and redundantly backed up as possible. He said that "distributed and disseminated systems are most reliable in most cases."


2. Risk of parallel systems, like gas and electricity, is additive. Eliminate gas and subtract that risk. Simple subtraction like I thought.



3. He said something which I didn't ask, but which is interesting -- he said that general range of annualized "acceptable risk" of catastrophic failure in most kinds of systems is ten to the minus 3 or 4 (compare to cancer ten to the minus 1, car accident ten to the minus 2). Ten to the minus 4 is 1 in 10,000. Seems like a low bar for catastrophic explosions, but that's what it is.




That's about it. What did we learn?

[Pelagic]

"That's about it. What did we learn?'

That we don't need to buy a canary or wear rubber boots!

[Adelie]

Originally Posted by Dockhead

The risk of shock goes up with DC voltage, and 24v is the highest which is generally considered more or less safe -- as far as I understand. A 48v system, as far as I understand, needs a different level of protection against shock.


But fire risk is for sure less with higher voltages, so it's a balancing act. Higher voltage means more efficient power transmission, too.

60V DC is generally considered the limit. Just over 20yr ago there was movement to go to 42v for automobiles. At 48v the charging voltage would have been high 50s but during cold weather would have gone over 60v. So they chose 42v so that 60v would never be exceeded.
https://en.wikipedia.org/wiki/42-volt_electrical_system

This is why most small marine electric propulsion systems are 48v, it uses an interger number of 12v batteries and only in somewhat unusual conditions exceeds 60v. The tradeoff between performance and liability is acceptable for this small a market.

[mako]

So from a practical point of view, what is the advantage of a 48V system? You can use smaller wires to run 20ft to your windlass, saving $50... but the alternator costs $1000 more!

[Adelie]

Originally Posted by makobuilders

So from a practical point of view, what is the advantage of a 48V system? You can use smaller wires to run 20ft to your windlass, saving $50... but the alternator costs $1000 more!

48v is what you do if you have electric propulsion. Even for short runs at 12v, the cabling would be huge for the required amperage. Also, I believe there are other gains, I believe the motor gets smaller, not sure. If you are doing 48v you can run an inverter directly off of that and use a step down to run 12v for everything else.

If you want to run 48v to the windlass, yes, you can use smaller cabling, but then you need to find a windlass that runs on 48v. I don't know how easy or hard that would be.

For charging 48v you would use an off the shelf MPPT. If you are running electric propulsion, you also have the real estate to support the solar charging, or you wouldn't be doing it in the first place. If you aren't doing electric propulsion then there is no need to go to 48v, 24v is plenty.

[Pelagic]

"For charging 48v you would use an off the shelf MPPT. If you are running electric propulsion, you also have the real estate to support the solar charging, or you wouldn't be doing it in the first place. If you aren't doing electric propulsion then there is no need to go to 48v, 24v is plenty."

I would also think that a 48v system would limit you to using only high voltage panels and even then, nearing sunset, would not the voltage be too low to be captured?.

[rslifkin]

You could run panels in series to get the voltage up. And don't MPPT controllers have the ability to step voltage up?

[Pelagic]

Originally Posted by rslifkin

You could run panels in series to get the voltage up. And don't MPPT controllers have the ability to step voltage up?

I guess series would work if partial shading was not an issue.

I don't know if my Outback has the ability to step up as it's never been an issue.

My Sunpower panels in parallel show about 64VDC coming in during peak sunlight, but down to around 42VDC around 4-5pm

Not a problem as I am a 24V system

[Adelie]

Originally Posted by Pelagic

"For charging 48v you would use an off the shelf MPPT. If you are running electric propulsion, you also have the real estate to support the solar charging, or you wouldn't be doing it in the first place. If you aren't doing electric propulsion then there is no need to go to 48v, 24v is plenty."

I would also think that a 48v system would limit you to using only high voltage panels and even then, nearing sunset, would not the voltage be too low to be captured?.

3 to 5 identical panels in series will give you 70v-100v depending on the specific panels which the controller will step down to correct charging voltage.

https://www.victronenergy.com/solar-charge-controllers

[seandepagnier]

Originally Posted by Adelie

48v is what you do if you have electric propulsion.

48v is more a compromise of motor and controller efficiency as well as voltage drop in wiring more than anything to do with safety from shock. The voltage that is safe from shock on a wet boat is maybe 24 volts.. maybe not if you are standing in water.

A lot of ev systems in a similar power range use voltages around 48, like forklifts, ebike etc run at 36-60 volts. For higher performance, higher voltage is used with the risk of blowing the electronics (if you don't change them)

At low voltages, motor controller and motor has low efficiency. At higher voltages it's difficult to find mosfets with as good of efficiency, and the motor losses also become higher. The best efficiency for motors and controllers in the range 2-10kw is usually around 60 volts.

It seems efficiency tradeoff is mostly when volts and amps are comparable. 12 volts and 200 amps is not ideal, and 200 volts with 12 amps not efficient either, but 200 volts makes sense at 200 amps.

I used 12v for propulsion years ago with trolling motors. Up to 3 knots boat speed and up to 70 amps at 12 volts. I normally went 1.8 knots using 22 amps 12 volts. This was not an efficient motor, but no problem to transmit for the 00 gauge aluminum wire I got for free.

For mppt, I am building my own because I want to buck or boost the voltage, and get the highest possible efficiency for each panel, and the cost of commercial mppt is very high for what it actually cost to build an mppt capable of 250 watts which is under $10.

[kefroeschner]

Orion is all electric -- 570 Ahr Pb-acid bank, 2 8kW inverters, a two hob induction stove, Sharp Carousel convection/ microwave, water heater, etc. Total of 800 watts rated PV panels. We run fine with no generator or shore power. Cook big meals, have hot water for showers. No flammable fuels anywhere. No smelly engine in the bilge. We are getting ready for "The World -- After Oil."

[jmh2002]

Originally Posted by kefroeschner

Orion is all electric"

Do you have more links to your boat and it's setup?

[noelex 77]

Originally Posted by kefroeschner

Orion is all electric -- 570 Ahr Pb-acid bank, 2 8kW inverters, a two hob induction stove, Sharp Carousel convection/ microwave, water heater, etc. Total of 800 watts rated PV panels. We run fine with no generator or shore power. Cook big meals, have hot water for showers. No flammable fuels anywhere. No smelly engine in the bilge. We are getting ready for "The World -- After Oil."

This is a great set up, but for anyone thinking of duplicating the above it will only work in areas of reasonably good solar insolation.

It is important to understand this limitation and ensure it matches your cruising plans.

[kefroeschner]

We have posted before, but a long time ago. Finally getting more active. Maybe should make a web-site, but have not yet gotten a round 'tuit.'



Yes Expected Insolation should be considered, but it is rather surprisingly good almost anywhere you'd want to go. Northwest Passage excepted. We are also testing a pendulum driven system to charge batteries from the pitch and roll of the boat. This would supplement the PVs on gloomy days. No results yet.